Color-shifting foil and wide security threads used in banknotes are known primarily for use in the security industry; for example foils are used either their ability to produce color-shifting flakes or as is to produce various security documents. Color-shifting foil is also used for decorative purposes. In some instances sheets of opaque foil are bonded to other articles to provide enhancement or security features. Thread that is embedded or laminated as a single strand into a banknote provides a way in which the bank note or document can be authenticated. However banknote threads of the type used in Canadian currency are visible from a single side and provide a color shift on a single side of the banknote. Only one color in a given instant is visible to a viewer as the thread is essentially planar. As the banknote is tilted with respect to the viewer, the color changes and a color shift occurs.
U.S. Pat. No. 5,974,150 teaches the weaving of dichroic fibers to make a label having security features.
The term color-shifting textile used hereafter is to refer to as being a material made of plural color-shifting strands that are woven, knitted, knotted, or braided, and wherein the plural strands, essentially form the fabric, or a single strand that is woven into several rows of a warp in an alternating fashion.
In most applications where it is desirable to provide a color-shifting appearance, the color-shifting effect is either applied by way of coating the article with a paint or ink containing color-shifting flakes or alternatively by adhering a sheet of color-shifting foil to the article.
Although these methods serve their purpose, it is desired to fabricate an article out of color-shifting strands which are durable and which exhibit a color shift from either side.
It is an object to provide color-shifting strands, whereby the strands serve as plural rows of a weft and can be woven into a warp to yield an integral color-shifting article, and whereby the color-shifting strands form the article itself.
The color-shifting material may be a single strand of material having sufficient strength or may be itself be combined with other strands to provide a stronger material, such as formed into combined threads producing yarn, string or rope with color-shifting effects.
Continuous work is ongoing to improve the appearance and performance of coatings. Opaque, inorganic based color-shifting Fabry-Perot structures have been used for years and have excellent color-shifting visual effects. Foils having a release layer coated with thin film coatings are often used to harvest flakes from the coated substrate. Typically, structures of this type in the form of foils are made by depositing upon a substrate coated with a release layer, a reflector layer, followed by a dielectric layer followed by an absorber layer. These opaque foils appear highly reflective from one side due to the presence of a reflector layer and appear highly reflective with a color that changes in an angle dependent manner when viewed from the opposite side due to the Fabry-Perot structure. Foil can be comprised of a substrate coated on both sides with a symmetric Fabry-Perot structures of the type Ref/Diel/Abs.
Although such foil coated on a single or both sides is very useful for example in the making of flakes, or simply as a decorative foil, this invention provides products heretofore not known which are useful as threads such as threads in banknotes or narrower threads or strands for weaving into a textile.
In a preferred embodiment a strand is formed from an elongate strands of foil that are less than 500 microns in width which serve as single strand yarn or can be combined into multiple strand yarn for weaving a textile product such as a color-shifting label.
In accordance with this invention a high quality strand having a required strength is provided providing a high degree of chroma and strong color-shifting effects seen from either side, when the object or light source upon the object is moved.
In accordance with this invention, an opaque color-shifting strand is provided, wherein the structure comprises an organic support layer and; a) a single or double period Fabry-Perot structure on a single side of the organic support layer, or, b) two single or a double period Fabry-Perot structure sharing the same reflector layer on one side of an organic support layer or c) an optically variable color-shift ink on one side of an organic support layer.
In accordance with an aspect of this invention these strands preferably each have width “w” of less than 500 microns, and a thickness “t” of more than 6 microns. The organic support layer provides rigidity for preventing the color-shift coating from curling, for allowing precise cutting of the strand substrate into discreet strands of a predetermined size and or lessening chipping and breaking of the interference coatings.
In an alternative embodiment, the opaque color-shifting strand is embossed with a diffractive microstructure providing a strand that shows opaque color-shifting by thin film and diffractive light interference simultaneously. This combined interference is disclosed in U.S. Pat. No. 6,841,238 related to chromatic pigments and foils.
In accordance with an aspect of this invention, an opaque color-shifting woven structure is provided, comprising a plurality of color-shifting strands, wherein the strands each comprise an organic support layer carrying on one side or each side thereof, a reflector layer, a dielectric layer and an absorber layer, said strands each having an width of less than 500 microns, and a thickness of more than 6 microns, the organic support layer providing rigidity for preventing the strands from curling and for lessening chipping and breaking of the strands.
In accordance with this invention a color-shifting product is provided wherein the product is comprised of a plurality of interwoven color-shifting strands, and wherein the product has a greater tensile strength than is obtained from a single strand of color-shifting material and wherein different colors from different strands are seen simultaneously.
In accordance with the invention an interwoven color-shifting textile is provided comprising plural color-shifting strands forming a weft supported by a warp.